A composition containing an alkali-soluble resin and a naphthoquinone diazide compound as a photosensitive substance has been generally used as a positive type photo-resist composition. For instance, U.S. Pat. Nos. 3,666,473, 4,115,128, and 4,173,470, etc. disclose "novolac type phenol resin/naphthoquinone diazide substituted compound" and L. F. Thompson discloses in "Introduction to Microlithography" (ACS Publisher, No. 2, Vol. 19, pp.112-121) discloses an example of "a novolac resin comprising cresol-formaldehyde/sulfonic ester of trihydroxybenzophenone-1,2-naphthoquinone diazide" as the most typical composition.
In such a positive photo-resist basically comprising a novolac resin and a quinone diazide compound, the novolac resin provides high resistance to plasma etching and the naphthoquinone diazide acts as a dissolution inhibitive compound. In addition, the naphthoquinone diazide forms a carboxylic acid when undergoing a light irradiation, thereby losing the dissolution-inhibiting ability, to enhance the alkali solubility of the novolac resin.
Up to date, various positive photo-resists containing a novolac resin and a naphthoquinone diazide photosensitive substance have been developed and put into a practical use from such a viewpoint, and they have sufficient results in a line width process of approximately 0.8 to 2 .mu.m.
However, an integrated circuit increasingly has an enhanced integration degree, and in the production of a semiconductor substrate such as a super LSI, it has been required to process a super fine pattern comprising a line width of half micron or less. In order to attain the required resolution, a wavelength of the exposing machine used in a photographic lithography has become more small wavelength. At the present, the use of a far ultraviolet ray or an excimer laser ray (e.g., XeCl, KrF, ArF, etc.) has been considered.
However, when the conventional resist comprising a novolac and a naphthoquinone diazide compound is used for the formation of a lithographic pattern with a far ultraviolet ray or a excimer laser, since the novolac and the naphthoquinone diazide have strong absorptions at a far ultraviolet region, the light is difficult to arrive at the bottom of the resist and, thus, only a low sensitive pattern having a taper can be obtained.
As one means for solving the problem, U.S. Pat. No. 4,491,628, European Patent 249,139, etc. disclose chemically amplified resist compositions. The chemically amplified positive type resist composition is a pattern-forming material in which an acid is formed on an exposed portion with the irradiation such as far ultraviolet ray, and the solubilities in a developer on the radiation-exposed portion and the unexposed portion are caused to be changed by a reaction with the aid of this acid, thereby forming a pattern on a substrate.
Examples which can be mentioned include a combination of a compound which generates an acid by photochemical decomposition with an acetal or O, N-acetal compound (JP-A-48-89003; the term "JP-A" as used herein means Japanese unexamined patent publication), a combination of a compound which generates an acid by photochemical decomposition with an ortho ester or amide ester compound (JP-A-51-120714), a combination of a compound which generates an acid by photochemical decomposition with a polymer having an acetal or ketal group in the main chain (JP-A-53-133429), a combination of a compound which generates an acid by photochemical decomposition with an enol ether (JP-A-55-12995), a combination of a compound which generates an acid by photochemical decomposition with an N-acylimino carbonic acid compound (JP-A-55-126236), a combination of a compound which generates an acid by photochemical decomposition with a polymer having an ortho ester group in the main chain (JP-A-56-17345), a combination of a compound which generates an acid by photochemical decomposition with a tertiary alkyl ester (JP-A-60-3625), a combination of a compound which generates an acid by photochemical decomposition with a silyl ester (JP-A-60-10247), a combination of a compound which generates an acid by photochemical decomposition with a silyl ether (JP-A-60-37549 and JP-A-60-121446), etc. Since the quantum yield exceeds 1 in principle they exhibit a high sensitivity.
Similarly, examples of the systems which are stable with the elapse of time at room temperature but which are decomposed by being heated in the presence of an acid to show an alkali-solubility include combinations of a compound which generate an acid by exposure with an ester of a tertiary or secondary carbon (e.g., t-butyl or 2-cyclohexenyl) or a carbonate compound, for example, as described in JP-A-59-45439, JP-A-60-3625, JP-A-62-229242, JP-A-63-27829, JP-A-63-36240, JP-A-63-250642, Polym. Eng. Sce. Vol. 23, p. 1012 (1983), ACS. Sym. Vol. 242, p. 11 (1984), Semiconductor World, November (1987), p. 91, Macromolecules, Vol. 21, p. 1475, (1988), and SPIE, Vol. 920, p. 42 (1988). These systems also possess high sensitivity and have a small absorption at a deep UV region in comparison with the naphthoquinone diazide/novolac resin; thus, they can be considered to be systems effective for shortening the wavelength of the light source described above.
The positive type chemically amplified resists described above can be roughly classified into three-component systems comprising an alkali soluble resin, a compound which generates an acid through exposure with irradiation (a photo-acid generator) and a dissolution inhibitive compound which becomes alkali-soluble by a catalytic reaction with an acid (an acid-decomposable dissolution inhibitive compound), and two-component systems comprising a resin possessing a group which becomes alkali-soluble by a reaction with an acid and a photo-acid generator.
The two-component or three-component positive resist of chemical amplification type forms a resist pattern by undergoing decomposition upon heat treatment in the presence of the acid generated from a photoacid generator by exposure and then being submitted to development. The positive resist of such a type has a problem such that, in proportion to the standing period from exposure to heat treatment (PEB treatment), the generated acid diffuses farther and the acid situated in the surface part of the resist is subject to inactivation by basic impurities in the atmosphere, thereby causing changes in not only sensitivity but also profile (T-top shape) and line width of a resist pattern obtained after development. In particular, the lowering of sensitivity and the formation of a T-top shape come into a great problem in the case of acid decomposable groups of the type which are relatively large in activation energy required for acid decomposition, such as a t-BOC group and a t-butylester group. On the other hand, acid decomposable groups of the type which are small in activation energy required for acid decomposition, such as an acetal group, a tetrahydropyranyl ether group and a silyl ether group, offer a problem of thinning the line width of a resist pattern although they can mitigate the aforementioned drawbacks. Further, those groups produce the phenolic OH groups upon acid decomposition, and thereby the dissolution accelerating effect is rendered insufficient; as a result, solubility discrimination between before and after exposure becomes insufficient. Thus, the resolution and the defocus latitude obtained thereby are still insufficient.
As means to solve such problems, the arts of using groups capable of producing a carboxylic acid in the presence of an acid generated are disclosed in JP-B-02-27660 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-05-181279 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-06-83059, JP-A-06-282073 and European Patent 366,590.
However, as previously mentioned, those arts are still unsuccessful in reducing a change of pattern shape (formation of T-top) and a variation (lowering) of sensitivity due to a lapse of time after exposure.
On the other hand, the arts of using the resins having groups which are liable to decompose by the action of an acid (small in activation energy required for acid decomposition) and hard to cause a change in pattern shape and a variation of sensitivity are disclosed in JP-A-02-25850, JP-B-03-44290, JP-A-04-211258, JP-A-05-19482, JP-A-05-249682, JP-A-06-167811, JP-A-06-273934 and European Patent 447,868.
However, dissolution accelerating effect cannot be produced by those arts; as a result, the solubility of exposed areas in an alkaline developer becomes insufficient, and so the resolution and the pattern profile obtained are not satisfactory.